Originally Posted by The Devo
will it even be worth the trouble to coach them?
Many people have a "the customer is king/right" attitude. Forget about those guys. It's often not worth it. Especially if things turn out more difficult for you (because they want lots of changed) they will just feel reinforced in their thinking that listening to you was a bad idea.
Sometimes you find clients who really appreciate your input and with whom you can actually work TOGETHER! Keep those, drop the rest, unless they know what they want and can describe it in reasonable terms. Build yourself a client base with people you're comfortable to work for and stick to those whenever possible.
Having good people skills, lots of patience and the ability to explain and break down artistic/technical issue in plain English helps.
And do EVERYTHING in writing. Verbal "handshake" deals can become your worst enemy. Archive all correspondence. I used to encounter some bad apples when I did freelance who'd drag out payment forever. Good I had all correspondence archived. Got my money in the end.
Have some terms of service set up and put on the contract - e.g. when payment is due (usually within 30 days - reliable clients can get up to 60). Agree how and when the money should be received.